This invention relates to a process for the preparation of chloroform (CHCl.sub.3), starting out from carbon tetrachloride (CCl.sub.4)
There are references in the literature concerning several methods for reducing the halogen content of a range of organohalogenated compounds. Nevertheless, the majority are impractical and of no commercial interest because of their excessive sophistication.
As a result of the declining market for carbon tetrachloride, there is a growing excess of this product. In view of this situation, researchers are trying to revalue this product by searching for methods allowing it to be used as a raw material for the manufacture of chloroform, the market demand for which is, on the contrary, growing.
Thus, the Dow Chemical Co. U.S. Pat. No. 2,886,605 of 1959 teaches a method of hydrodehalogenation of polyhalogenated hydrocarbons, using a cuprous chloride catalyst in a fluidized bed. The greatest drawback of this method for commercial exploitation is that it is run at so high temperatures (350.degree. C. to 550.degree. C.) that such an abundant carbonization occurs that it becomes necessary continuously or very frequently to regenerate the catalyst.
Another Dow Chemical Co. patent (U.S. Pat. No. 3,579,596 of 1971) teaches a process for producing chloroform from gas phase carbon tetrachloride, using a fixed catalyst bed of platinum on a substrate. This method, nevertheless, suffers from serious limitations, for example, that
a) the need to use excessively high amount of hydrogen relative to a stoichiometric amount encourages the production of methane and, furthermore, extraordinarily hinders the recovery of the reaction products, and PA1 b) The reaction is highly exothermic (.DELTA.H=-22.70 kcal/ mol, at 400 K, for a 100% theoretical selectivity of chloroform production), making it very hard to control the temperature. According to trials carried out by the inventors, hot spots are formed in the catalyst in the gas phase process, encouraging the formation of free radicals which, in turn, give rise to the formation of heavy polychlorinated compounds. When these are deposited on the catalyst surface they almost immediately and irreversibly deactivate it.